1. Field of the Invention
The field of this invention relates to an integrated circuit device, an electronic device comprising frequency signal generation circuitry, and a method therefor. The invention is applicable to, but not limited to, a method for compensating for frequency drift within a controllable oscillator.
2. Description of the Prior Art
Wireless communication systems, such as the 3rd Generation (3G) of mobile telephone standards and technology, are well known. An example of such 3G standards and technology is the Universal Mobile Telecommunications System (UMTS™), developed by the 3rd Generation Partnership Project (3GPP™) (www.3gpp.org). The demanding technical specifications required of a wireless telecommunication handset that support, for example, a wideband code division multiple access (WCDMA) air interface, such as may be found within a UMTS™ network, mean that synthesiser oscillators, such as voltage controlled oscillators (VCOs) or digitally controlled oscillators (DCOs), within a transceiver of such a handset must have excellent phase noise performance.
However, such wireless telecommunication handsets are required to maintain calls for extremely long periods of time. As a result, the handset's transceiver synthesisers must be capable of maintaining a frequency lock over a wide range of temperatures. Oscillators exhibit an inherent frequency drift, due to changes in operating temperature. Such a drift is hard to reduce below 40 ppm/degC. If temperature-related frequency drift were to be compensated by way of the main control port of the oscillator, for example through a conventional phase locked loop (PLL), the oscillator would require a substantial control gain (Kco). As noise on the control port is converted to oscillator phase noise, such a substantial control gain typically results in high oscillator phase noise. This is not compatible with the requirement of an excellent phase noise performance, such as is required for a wireless telecommunication handset supporting WCDMA. Generally, it is difficult to implement a wide control range without also introducing an unacceptable degradation of phase noise performance.
Known solutions to this problem typically utilise a temperature-dependent voltage signal applied to an auxiliary varactor within the oscillator (via an auxiliary control port thereof) in order to minimize oscillator frequency variations that are caused by changes in temperature. In this manner, the need for the adjustment range of the main control port of the oscillator to be sufficiently large enough to allow for such frequency variations caused by changes in temperature is substantially alleviated. As a result, the oscillator may be provided with a significantly reduced control gain (Kco), thereby reducing the phase noise of the oscillator.
However, a problem with such a solution is that the use of an auxiliary varactor with a temperature-dependent voltage signal requires accurate modelling of temperature behaviour, and typically still requires sufficient adjustment range within the main control port of the oscillator to allow sufficient margin for error. Additionally, it is difficult to generate a temperature-dependent voltage in such a manner that said voltage has low noise. Therefore, such a solution typically requires significant filtering of the temperature-dependent control voltage in order to reduce phase noise to acceptable levels.
Thus, a need exists for an improved apparatus for compensating for frequency drift within an oscillator, and method of operation therefor.